This invention relates to low dielectric constant layers for use in various applications. The invention also relates to methods of forming low dielectric constant layers in a wide range of VLSI fabrication operations.
As the features of microelectronic integrated circuits devices are reduced to smaller sizes, the electrical properties of the materials that constitute the devices will require change and improvement. One material that must be improved is the electrical insulator (“dielectric”) used between the wires, metal lines, and other elements of the circuit. Without improvement in the insulator material, there will be increased problems due to capacitive effects such as coupling (crosstalk) and propagation delay. The speed at which future circuits will operate will be limited by RC delay in the interconnect.
These difficulties can be mitigated by preparing the circuit using an inter-layer dielectric (“ILD”) having a dielectric constant that is as low as possible. For integrated circuits that are fabricated using a damascene or dual damascene method, the ILD is composed of an insulating material and a copper diffusion barrier film. Although it is important for both the insulating material and the copper diffusion barrier film to be formed of materials having a low dielectric constant, the present application is mainly directed to methods and devices for producing a copper diffusion barrier film having a low dielectric constant.
Silicon nitride provides a film having satisfactory properties as a copper diffusion barrier, but its dielectric constant is relatively high. Therefore, some prior art has involved doping silicon nitride with a material having a lower dielectric constant. For example, some previous methods for producing a copper diffusion barrier with a low dielectric constant have involved doping silicon nitride with boron. Although boron-doped silicon nitride has a lower dielectric constant than pure silicon nitride, it has proven to be unstable in the presence of atmospheric moisture. Over time, the dielectric constant of boron-doped silicon nitride tends to increase, rapidly becoming unsuitable for use as a low dielectric constant copper diffusion barrier. Improved materials and processing are required.